Electronic cigarettes are substitutes of cigarettes. Electronic cigarettes can simulate the taste of cigarettes, but smoking electronic cigarettes does not generate harmful tar, nicotine and second-hand smoke. Therefore, electronic cigarettes can improve smoking cessation success rate of nicotine replacement therapy. A conventional electronic cigarette generally comprises two parts, wherein one part is an electronic cigarette rod simulating a cigarette rod, and includes a smoke sensor and a battery circuit received therein; and the other part is an atomizer connected with the electronic cigarette rod, the atomizer comprises an oil reservoir provided with air holes, fiber cotton, and a heating wire. The fiber cotton coils around the heating wire, and the fiber cotton and the heating wire are accommodated in the oil reservoir together. The oil reservoir is filled with special tobacco tar, and the tobacco tar penetrates into the fiber cotton layer by layer. The heating wire can be electrified and then generates heat. When the heating wire generates heat, the heating wire can bake the oiled fiber cotton contacting therewith, so that the tobacco tar is volatilized and become smoke. The smoke is inhaled by a user via a suction nozzle, and an action of simulation of smoking is completed. However, in the prior art, the tobacco tar in the atomizers of the electronic cigarettes has a risk of penetrating into the electronic cigarette rods. Thus, the electronic cigarettes cannot achieve good effect of preventing tobacco tar leakage, and lives of batteries of the electronic cigarettes may be adversely affected.